This application claims the priority of Korean Patent Application No. 2003-11639, filed on Feb. 25, 2003, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a light-receiving device with a high response speed and a method for manufacturing the same. The present invention also relates to an optoelectronic integrated circuit (OEIC) comprising the light-receiving device.
2. Description of the Related Art
An advantage of using a silicon semiconductor substrate is that it ensures excellent reliability and allows highly integrated density in integrating a logic device, an operation device, and a drive device on the substrate. Also, a silicon semiconductor material can be used in fabrication of a highly integrated circuit at a much lower cost than a compound semiconductor material, due to use of an inexpensive silicon. Therefore, silicon (Si) is most often used as a basic material in integrated circuit fabrication.
Due to a light-receiving device made of silicon, various optoelectronic integrated circuits (OEICs) such as a silicon optical bench with a monitor photodetector (MPD) for monitoring an optical power from a light source and an optical module for optical communication or optical pick-up with modulated light source and photodetector can be obtained.
In order for realizing OEICs and realizing further various applications, the light-receiving device must satisfy a high response speed.
A response speed in a light-receiving device, that is, a photodetector, depends on a transit time of holes and electrons in an intrinsic region (a depletion region) and a diffusion time of holes and electrons outside a doped region.
Diffusivity of carriers in silicon can be obtained according to the Einstein relation as represented by Equation 1:D/μ=kT/q,  Equation 1
wherein, D is diffusivity of carriers, μ is mobility of carriers, k is the Boltzmann constant, T is a temperature (K), and q is a charge.
In an intrinsic silicon (Si), the mobility of electrons is 1350 cm2/Vs (where, V is a voltage (volt) and s is a time (second)) at room temperature (300 K) and the mobility of holes is 450 cm2/Vs. The mobility of holes is much less than that of electrons. Therefore, it can be seen from the Einstein relation that the diffusivity of holes is less than that of electrons.
While a built-in potential (caused by an electric field generated in an intrinsic region without an external voltage) is increased for increasing the intensity of an electric field applied to an intrinsic region, and a doping concentration is increased for enhancing the electroconductivity of a doping layer, the mobility of holes further decreases with increase of the built-in potential and doping concentration. Therefore, in order to accomplish a high response speed in a PIN photodetector, the thickness of a P region, through which holes with slow mobility travel, is required to be reduced.
Meanwhile, in an optical pick-up, a photodetector divided into several segments as shown in FIG. 1 is used to reproduce information recorded in optical information storage media, for example, an optical disc such as compact disc (CD), digital versatile disc (DVD), and next generation DVD (e.g. Blu-ray disc (BD) and/or Advanced optical disc (AOD) and detect an error signal, for example, a focus error signal and a tracking error signal during recording and/or reproduction operation. FIG. 1 shows a 4-division photodetector for optical pick-up, but a photodetector for optical pick-up can have various division structures.
Referring to FIG. 1, when A, B, C, and D indicate segments of the 4-division photodetector 1 and respective signals detected at each segment, as well known in the optical pick-up pertinent art field, a focus error signal (FES) according to the astigmatism method and an information reproducing signal (RF signal) are equal to (A+C)−(B+D) and A+B+C+D, respectively. A tracking error signal (TES) according to the push-pull method is equal to (A+B)−(C+D).
As described above, a photodetector having a plurality of segments is used in optical pick-up. As a large storage capacity and high-speed data processing of optical information storage media are required, use of a photodetector with a high response speed and a low noise for excellent sensitivity is required in an optical pick-up. However, a conventional photodetector with an n-division structure cannot satisfy a high response speed and a low noise. Therefore, fabrication of various devices requiring high integrity, for example, fabrication of an integral structure of a photodetector with a photodetector integrated circuit (PDIC) is faced with many problems.